As for a hybrid electric vehicle and an electric vehicle, a high-power brushless motor is used. Furthermore, a higher power motor will be expected. To control the brushless motor of a hybrid electric vehicle, it is necessary to accurately ascertain the rotation angle of an output shaft of the motor. This is because the rotation position (angle) of a rotor needs to be correctly ascertained in order to control switching of energization of coils of a stator.
Accordingly, the motor preferably includes a resolver to accurately detect the angle. Such resolver used in a drive mechanism of a vehicle is required to provide high accuracy in addition to environment resistance because of the high number of revolution of the drive mechanism. As with other in-vehicle components, the resolver is also demanded to achieve size reduction and cost reduction.
For increasing the accuracy of the resolver, a method using “skew” is conceivable. Specifically, methods for preventing distortion of a sine wave output from a magnetic resolver include a method of changing magnetic pole pitches of a rotor core and a stator core and a skew method of placing a stator core in an oblique position with respect to a rotor core (see JP 5(1993)-312590A).
On the other hand, a printed circuit has been known to reduce the size of a resolver. A pattern pitch in an arranging direction of a sheet coil to be provided on a base plate is adjusted to an irregular pitch, thereby preventing a higher harmonic wave from overlapping an electromotive waveform to enhance detection accuracy (see JP 7(1995)-211537A).
Furthermore, there is a sheet coil type resolver in which an excitation phase coil includes a spiral coil provided on a front side of an insulation sheet layer and a spiral coil provided on a back side and wound in a reverse direction from the front-side coil when the back-side coil is viewed in the same direction as the front-side coil, and a detection coil includes a spiral coil provided on a front side of an insulation sheet layer and a spiral coil provided on a back side and with an electrical phase difference of 90° from the front-side coil, the excitation phase coil and the detection coil being placed to face each other through a gap and to be relatively movable. The spiral coil of the excitation phase coil is formed of joining of a circular conductor and a linear conductor or formed in a wound form connected to a circular or linear conductor. The front-side spiral coil and the back-side spiral coil of the detection layer coil are connected in sequence to a half sine wave conductor and a circular or linear conductor. This configuration is able to reduce displacement errors and provide a resolver with little angle error (see JP 8(1996)-292066A).
However, from the viewpoint of cost reduction of the resolver, the use of the spiral coils is undesirable because such configuration inevitably requires a winding process during manufacture. Cost reduction is therefore not easily realized.
The use of windings additionally requires a process of winding a wire on a bobbin and a process of mounting a coil and increases the number of resolver components. This is an impediment to the cost reduction. The coil also requires a certain level of thickness and hence thickness reduction is also difficult.
On the other hand, when a printed circuit is adopted, the use of a sheet coil can realize thickness reduction. However, the electromotive force waveform becomes a stepped sine waveform because of the use of the sheet coil. Thus, a cyclic error component is picked up on a detection side, causing a detection error.
This would cause a problem that accuracy improvement is difficult. To increase detection accuracy, it is conceivable to adopt the aforementioned “skew”, but it is not directly applicable due to differences in shape.
In the case of adopting a configuration disclosed in JP 8(1996)-292066A, the detection accuracy can be increased but noise is not completely eliminated.
In detecting cyclic error components on the detection side, several peaks appear as seen in a graph showing relation between sensor error and error order (see FIG. 7 mentioned later). Even this method could only provide such an advantageous result that eliminates one of the peaks. Under present circumstances, there is a demand for detection accuracy improvement using other methods.
The present invention has a purpose to provide a thin-shaped resolver with increased accuracy.